An inflammatory response occurs in animals when cells or tissues are injured by bacteria, trauma, toxins, heat, or other agents, which can be collectively referred to as “Inflammatory Agents.” The nature and character of a given inflammatory response is regulated by the complex interaction of a variety of pro-inflammatory or anti-inflammatory stimulators or mediators, which are synthesized and released by cells and tissues. Some known species of pro-inflammatory or anti-inflammatory stimulators or mediators include cytokines, nitric oxide, thromboxanes, leukotrienes, phospholipids like platelet-activating factor, prostaglandins, kinins, complement factors, coagulation factors, superantigens, monokines, chemokines, interferons, free radicals, proteases, arachidonic acid metabolites, prostacyclins, beta endorphins, myocardial depressant factors, anandamide, 2-arachidonoylglycerol, tetrahydrobiopterin, cell fragments and chemicals including histamine, bradykinin, and serotonin. The discovery of new (i.e., previously unrecognized) species of pro-inflammatory or anti-inflammatory stimulators or mediators is an ongoing process.
The nature and intensity of inflammatory responses differ, depending on the site which has been invaded, and on the character of the Inflammatory Agent(s), and the interaction of pro-inflammatory or anti-inflammatory stimulators or mediators involved. The inflammatory response, when regulated and localized, is beneficial. If not regulated and generalized, however, the inflammatory response can cause significant tissue injury and even death.
Cytokines are one class of proteins produced predominantly by macrophages, monocytes, neutrophils and lymphocytes typically in response to a viral, bacterial, fungal or parasitic infection, as well as in response to T cell stimulation during an immune response. Cytokines are known to be synthesized by other cell types, such as stromal cells like fibroblasts, endothelial cells and smooth muscle cells, as well as epithelial cells, keratinocytes and hepatocytes. Cytokines are normally present in very low concentrations in the blood or tissues.
The structures and activities of cytokines have been the subject of many studies. It has become apparent that cytokines possess a wide spectrum of immunological and non-immunological activities. Cytokines affect diverse physiologic functions, such as cell growth, differentiation, homeostasis and pathological physiology. The art shows that cytokines have multiple biological activities and interact with more than one cell type. Cytokines are also known to be capable of stimulating their own synthesis, as well as the production of other cytokines from a variety of cell types. This phenomenon is called the “cytokine cascade.” Cytokine cascades are often associated with systemic changes arising from infection and tissue injury and, in this context, they serve a myriad of biological functions. For example, various cytokines, categorized as the interleukins (IL), interferons (IF), and tumor necrosis factor (TNF), are produced during immune and inflammatory responses. These cytokines beneficially control various aspects of these responses. In this situation, the cytokine cascade mediates normal host defense responses, cell regulation, and cell differentiation.
Under cascade circumstances, the function of cytokine production can become disordered. This disorder can lead to the presence of larger than normal concentrations of cytokines. When the cytokine cascade becomes disordered, there can be a rapid extension and amplification of the intended localized host response in such a way that only one or a few initiating stimuli trigger the eventual release and participation of scores of host mediators. Although a number of features of the host response assist in fighting off invasion, an overly robust or poorly modulated endogenous response can rapidly accelerate to produce other profound alterations in host homeostasis at the cellular, tissue, and systemic levels. As a result, cytokine expression in a region of the body where tissues or organs are legitimately subject to bacterial infection or an immune response challenge, can, when disordered, lead to unwanted destruction of healthy tissue elsewhere in the body. Larger than normal concentrations of certain cytokines can cause disease and other deleterious health effects, some of which can be lethal.
A disordered cytokine cascade that leads to the increased presence of the cytokines IL-1 and TNF can, alone or in combination, cause a state in animals clinically identical to systemic inflammatory response syndrome (SIRS), sepsis, and more severe variants of sepsis called severe sepsis (sepsis with organ dysfunction) and septic shock (severe sepsis with refractory hypotension). These conditions can arise due to the individual, combined, and concerted effects of a large number of cytokines. Severe sepsis and septic shock afflicts more than 750,000 Americans every year. Cytokine-induced sepsis can be brought about by infection by a variety of microorganisms, including not only bacteria but also viruses, fungi, and parasites. SIRS or sepsis can also be initiated by host response to invasion in general, such as by cancer or as a result of major surgery or trauma. Septic shock is a potentially lethal cytokine-mediated clinical complication against which there is no generally effective therapeutic approach.
One of the best studied examples of cytokine-induced septic shock is the case of infection by gram-negative bacteria. The appearance of bacterial endotoxins, such as lipopolysaccharide (LPS), in the host bloodstream is believed to lead to the endogenous production of a variety of host factors that directly and indirectly mediate the toxicity of LPS. These host-derived mediators include many now well-recognized inflammatory cytokines, as well as endocrine hormones, in addition to a number of other endogenous factors such as leukotrienes and platelet activating factor. Among the interacting factors that together comprise the cytokine cascade, the cytokine TNF-alpha is believed to be the most important identified to date. During the ensuing cytokine cascade, the mediators that appear early in the invaded host are thought to trigger the release of later appearing factors. Many of the cytokine mediators not only exert direct functions at the targeted tissues, but also at other local and remote tissues, where subsequent responses to other mediators produced during the cascade occur, and so on. The result, if unchecked, can be a multifaceted pathological condition, which is characterized most prominently by deleterious hemodynamic changes, organ dysfunction and coagulopathy leading to multiple organ failure and, often, to death.
Multiple attempts have been made and still many others are currently underway to block specific mediators of this response. These attempts, however, have been relatively unsuccessful. Therapy aimed at single mediators cannot effectively attenuate the entire response. Furthermore, it is both the duration and intensity of inflammation that correlates best with outcome. Generally, higher concentrations of cytokines and longer duration of over-expression of proinflammatory cytokines are associated with higher mortality. Systemic inflammation results in organ injury which results in the prolongation of the inflammatory response and thus, more organ injury.
Similarly profound, but often less lethal, physiologic effects can occur as a result of abnormal production of certain cytokines, without the presence of exogenous bacterial toxins. As one example, cytokine TNF-alpha has been found to be an anti-tumor cytokine. As a result, TNF-alpha has been expected to be useful as an antitumor agent. However, it has been discovered that TNF-alpha is identical with cachectin, which is a cachexia-inducing factor. The disordered production of TNF-alpha has also been correlated with, not only severe sepsis and septic shock, but the incidence of rheumatoid arthritis, adult respiratory distress syndrome (ARDS), the severity of viral hepatitis, myocardial ischemia, and the inhibition of myocardial contraction. Also, TNF has recently been shown to be involved in initiating the expression of human immunodeficiency virus in human cells that carry latent virus, which could be a contributing factor in the expression of latent AIDS virus in certain individuals. Furthermore, a correlation between the TNF level in the blood and blood pressure has also been observed. As TNF levels increase, blood pressure decreases, which can lead to serious complications such as kidney failure. Hypotension and in severe cases, hemodynamic collapse or shock, can be caused by cytokines such as TNF through endothelial damage, leading to loss of fluid from the intravascular space to the surrounding tissues, as well as through TNF and other cytokine stimulation of inducible nitric oxide synthase, that leads to myocardial depression and peripheral vasodilation.
TNF-alpha has been observed to stimulate production of other types of cytokines, such as IL-1, etc. Cytokine IL-1 is known to be an important agent for inducing and transmitting the systemic biological response against infection and inflammation. IL-1 induces the usual, desirable responses observed in inflammation in general, such as fever, increase of leukocytes, activation of lymphocytes, and induction of biosynthesis of acute phase protein in liver. This cytokine is known to have a strong antitumor activity.
When IL-1 is produced in abnormally larger amounts, however, the result may contribute to the severity of chronic inflammatory diseases, such as rheumatoid arthritis. Thus, the abnormal activation of various cytokines such as the interleukins (IL) and tumor necrosis factor (TNF) is believed responsible for the tissue damage and pain that occurs in various inflammatory conditions like rheumatoid arthritis. In rheumatoid arthritis, levels of TNF, IL-1, IL-6 and IL-8 increase dramatically and can be detected in the synovial fluid. The cytokine cascade induced by expression of these cytokines results in depressed lipoprotein metabolism as well as bone and cartilage destruction.
As another example, the cytokine IL-6 plays an important role in antibody production in B cells. The cytokine IL-6 also is an important factor in body systems, e.g., the hematopoietic system, nervous system, and the liver, as well as in immune system. For example, IL-6 is effective for inducing proliferation and differentiation of T cells, inducing the production of protein at acute phase by acting on hepatic cells, and promoting the growth of cells in bone marrow.
A correlation between the abnormal secretion of IL-6 and various disease states (e.g., autoimmune diseases, such as hypergammaglobulinemia, chronic articular rheumatism, and systemic lupus erythematosus; the abnormal state of polyclonal B cells, as well as in the development of the abnormal state of monoclonal B cells such as myeloma cells; Castleman's disease accompanied with tumor of the lymph nodes, for which the cause is unknown; primary glomerular nephritis; and the growth of mesangial cells) has been observed.
As yet another example, in bacterial infections, cytokines such as IL-8 act as a signal that attracts white blood cells such as neutrophils to the region of cytokine expression. In general, the release of enzymes and superoxide anions by neutrophils is essential for destroying the infecting bacteria. However, if cytokine expression causes neutrophils to invade, for example, the lungs, release of neutrophil enzymes and superoxide anion can result in the development of adult respiratory distress syndrome (ARDS), which can be lethal.
Despite their diverse and myriad functions, most cytokines share one common feature. Although most cytokines are found in the size and molecular weight range of 8 to 80 kilodaltons, the majority of cytokines are within a narrow size and molecular weight range of 8 to 51 kilodaltons. This size characteristic is extremely important for the clearance of cytokines from the blood.
In disease states where the kidney has failed—which is often the case in septic shock-hemodialysis or hemofiltration membranes are used as substitutes for the glomerular membrane of the kidney. Artificial membranes, however, are severely limited in their ability to clear cytokines from the blood due to their inadequate porosity. In fact, the predominant mechanism by which these membranes remove cytokines in clinical practice is not filtration, but rather nonspecific surface adsorption (J. Am. Soc Nephrol 1999 Apr. 10(4): 846-53, Cytokine removal during continuous hemofiltration in septic patients, De Vriese A S, Colardyn F A, Philippe J J, Vanholder R C, De Sutter J H, Lameire N H). Typically these membranes have 0.5 to 2 square meters of surface area available for adsorption that becomes saturated within the first 30 to 90 minutes of treatment (Biomaterials Sep. 1999; 20(17):1621-34, Adsorption of low molecular weight proteins to hemodialysis membranes: experimental results and simulations, Valette P, Thomas M, Dejardin P). An improved external device taught in the art uses certain sorbent polymers to externally interact with blood to reduce levels of cytokines or other species of pro-inflammatory or anti-inflammatory stimulators or mediators in blood or physiologic fluids with significant specificity. See, U.S. Pat. Nos. 7,556,768; 6,416,487; and 5,904,663. While such methods are advantageous in treating certain inflammatory conditions, there is a need in the art for a simpler method that does not require use of an external removal device.